1. Field of the Invention
The present invention relates to methods and systems for monitoring radiation, such as, for example, neutron and gamma emissions of a nuclear reactor or from spent nuclear fuel. The invention also relates to methods for monitoring a nuclear reactor. The invention further relates to methods for rejecting noise and accepting signals from a communication channel.
2. Background Information
Every circuit that is employed to detect relatively small electrical signals, such as pulses, must inevitably face the problem of separating the desired signal from unwanted noise. The sources of noise can be numerous, with the solution often being elusive. Properly shielded and grounded signal cables are typically employed to isolate signals from noise sources, although such cables, alone, are often insufficient.
In the nuclear industry, for example, special radiation hard cable is frequently employed to send signals from radiation monitors back to associated electronics that amplify and monitor those signals. Quartz is a common insulating material employed in such cables because of its radiation resistance and low dielectric absorption to signals having relatively fast transitions. However, quartz is susceptible to noise generated by both piezoelectric and triboelectric effects. For example, flexing or vibrating the cable can produce voltages within the cable at the point of the movement. These unwanted voltage signals, in turn, appear at the associated electronics. Often, a circuit can separate out the noise based upon pulse height or pulse shape. However, if the noise pulse happens to mimic a radiation monitor signal, then it is falsely counted as such a signal.
Application Ser. No. 09/629,286 discloses a method and system, which identify the source of a signal from multiple detector sources. The time differential of two arriving signals is employed to distinguish those arriving signals from signals from other detectors, which are also connected to the same communication channel or cable. That method and system, however, are susceptible to spurious noise signals.
Accordingly, there is room for improvement.
The present invention has been developed in view of the foregoing and other deficiencies of the prior art. The invention employs the arrival time of detector signals on a cable as a way to determine which detector has produced a signal and, also, to reject pulses originating along the cable at points other than at the detectors.
Signal-monitoring equipment is employed at each end of a cable to which plural detectors are electrically connected. Each detector is at a unique differential distance from each of the two sets of equipment. For example, if four detectors are each connected to the cable, then the difference in cable length between any detector and each of the two sets of equipment is unique. As a further example, a first detector might be closest to a first preamplifier and furthest from a second preamplifier, while the opposite is true for the fourth detector. Hence, the time difference between signal detection at each preamplifier is unique for each detector location.
As one aspect of the invention, a method of monitoring a nuclear reactor comprises: monitoring the nuclear reactor with a plurality of radiation sensors having spaced apart attachments to a cable; providing signal processing equipment at each end of the cable for processing signals from the radiation sensors; establishing signal time intervals based upon differences in time of arrival of signals from the radiation sensors to the signal processing equipment at each end of the cable; producing a plurality of output signals each of which has an amplitude proportional to a difference in time of arrival of a signal to the signal processing equipment at each end of the cable; and rejecting output signals which have a difference in time of arrival outside of the signal time intervals.
As another aspect of the invention, a method of monitoring a nuclear reactor comprises: providing a plurality of radiation sensors having spaced apart electrical connections to a communication channel; providing signal processing equipment at each end of the communication channel to process signals from the radiation sensors; establishing a difference in time of arrival for signals from each of the radiation sensors to the signal processing equipment at each end of the communication channel; establishing a signal time interval for each of the differences in time of arrival; producing a plurality of output signals each of which is related to a difference between time of arrival of a signal at the signal processing equipment at each end of the communication channel; rejecting the output signals which have the difference between time of arrival outside of the signal time intervals; and employing the output signals which have the difference between time of arrival within one of the signal time intervals to monitor the nuclear reactor.
Preferably, the method includes producing the output signals having an amplitude proportional to the difference between time of arrival.
As a further aspect of the invention, a system for monitoring radiation comprises: a communication channel having two ends; a plurality of radiation sensors having spaced apart electrical connections to the communication channel; signal processing equipment at each of the ends of the communication channel to process signals from the radiation sensors; means for producing a plurality of output signals related to a difference between time of arrival of a signal at the signal processing equipment at each of the ends of the communication channel; means for rejecting the output signals which have the difference between time of arrival outside of a predetermined signal time interval for each of the radiation sensors; and means for monitoring radiation based upon the output signals which have the difference between time of arrival within one of the predetermined signal time intervals.
The means for producing may include timing analyzer means for measuring the difference between time of arrival.
As another aspect of the invention, a method of rejecting noise and accepting signals from a communication channel comprises: providing a plurality of sensors having spaced apart electrical connections to the communication channel; providing signal processing equipment at each end of the communication channel to process signals from the sensors; establishing a difference in time of arrival for signals from each of the sensors to the signal processing equipment at each end of the communication channel; establishing a signal time interval for each of the differences in time of arrival; producing a plurality of output signals each of which is related to a difference between time of arrival of a signal at the signal processing equipment at each end of the communication channel; rejecting the output signals which have the difference between time of arrival outside of the signal time intervals; and accepting the output signals which have the difference between time of arrival within one of the signal time intervals.
Preferably, the method includes employing a plurality of unique differences in time of arrival; and employing an acceptance window about each of the unique differences to form the signal time intervals.